I noticed a lot of people in here are saying they use starter/grower constantly. Although this won't harm your chickens, if it has amprolium or any other anti coccidiosis in it, there can be serious delayed health effect for hatched eggs or anything that eats the eggs. If you talk to the manufactures they will advise not to use the meat or eggs for 3 weeks after feeding.
The warning not on the bag as they assume you only feed to babies.
The duck feed however is fine.
Medicated chick starter contains amprolium. It's a very low dosage thiamine blocker. It is perfectly safe to eat eggs and meat from birds fed medicated starter. But it should not be fed long term, as it can cause thiamine deficiency.
Grower, all flock, and flock raiser feeds are safe for all ages, and may actually provide better overall nutrition than layer feed for flocks that get lots of treats, free range, or have birds of mixed ages or genders.